^I agree with advice above. Buffs and debuffs with mages and damage with warriors.
Things like mass weakness or mass curse do wonders, making DK attacks much less deadly.
I would also try to position blocking warrior as a bait, so that other one without block is rarely attacked.
In my playthrough my shield expert has 80% block rating and he would be a real sponge for DK attacks.
If really desperate, give good shield to other warrior too, even if he is two-handler expert. This would reduce DPS to hurt those DK, so this should only be used as last resort.
